serial: 8250_pci1xxxx: fix off by one in pci1xxxx_process_read_data()

These > comparisons should be >= to prevent writing one element beyond
the end of the rx_buff[] array.  The rx_buff[] buffer has RX_BUF_SIZE
elements.  Fix the buffer overflow.

Fixes: aba8290 ("8250: microchip: pci1xxxx: Add Burst mode reception support in uart driver for writing into FIFO")
Signed-off-by: Dan Carpenter <dan.carpenter@linaro.org>
Link: https://lore.kernel.org/r/ZZ7vIfj7Jgh-pJn8@moroto
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Author: Dan Carpenter

drivers/tty/serial/8250/8250_pci1xxxx.c

@@ -302,7 +302,7 @@ static void pci1xxxx_process_read_data(struct uart_port *port,
 	 * to read, the data is received one byte at a time.
 	 */
 	while (valid_burst_count--) {
-		if (*buff_index > (RX_BUF_SIZE - UART_BURST_SIZE))
+		if (*buff_index >= (RX_BUF_SIZE - UART_BURST_SIZE))
 			break;
 		burst_buf = (u32 *)&rx_buff[*buff_index];
 		*burst_buf = readl(port->membase + UART_RX_BURST_FIFO);
@@ -311,7 +311,7 @@ static void pci1xxxx_process_read_data(struct uart_port *port,
 	}
 
 	while (*valid_byte_count) {
-		if (*buff_index > RX_BUF_SIZE)
+		if (*buff_index >= RX_BUF_SIZE)
 			break;
 		rx_buff[*buff_index] = readb(port->membase +
 					     UART_RX_BYTE_FIFO);